重卡传动轴用高强7075铝合金热流变行为及径向锻造微观组织演变

Hot Deformation Behavior of High-Strength 7075 Aluminum Alloy for Drive Shaft of Heavy Truck and Its Microstructure Evolution in Radial Forging

为研究重型卡车轻量化传动轴用高强7075铝合金在径向锻造时的热变形行为,将大直径7075铝合金挤压棒料预热退火后,取样进行了不同变形条件下的等温压缩试验。分别考虑温度与应变速率对应变强化及软化的影响,构建了适用于中大型7075铝合金传动轴热加工的改进Hansel-Spittel本构模型。根据动态材料模型理论获得了7075铝合金的热加工图,并据此分析了7075铝合金棒料在典型径向锻造工艺中的组织变化。研究结果表明:改进Hansel-Spittel模型能更准确地模拟预热退火态7075铝合金的峰值和稳态流变应力,预测值与试验值的平均相对误差仅为2.71%;7075铝合金在温度为350~450℃、应变速率为0.01~10 s^(-1)范围内具有较高的热加工稳定性,高温及低应变速率的变形条件有利于材料的微观组织演化;预热退火态7075铝合金棒料在经过截面收缩率为55.6%的径向锻造工艺和T6热处理后,原始板条晶粒转变为细化大转角晶粒组织,抗拉强度提高至651 MPa,延伸率提高至12.5%,综合性能得到显著改善。

The hot deformation behavior of high-strength 7075 aluminum alloy,adopted for lightweight drive shafts of heavy trucks,during the radial forging process is investigated through isothermal compression tests at different deformation conditions.The test samples are collected from an extrusion shaft billet with a large diameter that is fully preheated.A modified Hansel-Spittel constitutive model of 7075 aluminum alloy,which takes into account the effects of temperature and strain rate on strain hardening and strain softening,is proposed to predict the hot forming process of drive shafts with a large diameter.The processing maps of 7075 aluminum alloy are established based on the dynamic material model,and microstructure evolution of the shaft billet of 7075 aluminum alloy during a typical radial forging process is analyzed with the processing maps.The research results indicate that the modified Hansel-Spittel model can accurately predict the peak flow stress and steady flow stress of preheated 7075 aluminum alloy,with an average absolute relative error of 2.71% between the experimental data and the predicted data.The processing maps show that 7075 aluminum alloy has high thermal stability in the temperature range of 350 to 450℃ and strain rate range of 0.01 to 10 s^(-1),and high temperature and low strain rate will benefit the microstructure evolution of 7075 aluminum alloy during the hot forming process.After a typical radial forging process that perform a cross-section contraction of 55.6% and a heat treatment of T6,the original elongated grains of the shaft billet recrystallize and transform into fine grains with large angle boundary,which respectively increase the tensile strength and the elongation rate of 7075 aluminum alloy to 651 MPa and 12.5%.The drive shaft manufactured from the operated shaft billet can have excellent comprehensive properties.